Some flights have been cancelled to and from Turkey after more than 160 people were killed in an attempted military coup.
Britons are being advised to stay indoors following a night of gunfire and explosions in Ankara and Istanbul and reports of shooting near the tourist resort of Marmaris.
British Airways cancelled all flights to and from the country on Saturday and the Foreign Office advised people to ‘stay indoors’ and to avoid public places.
A British Airways spokeswoman said: “In light of the events unfolding in Turkey, all flights to and from the country have been cancelled today (July 16).
“We are keeping flights to Turkey under review.”
Customers affected by the cancellations are being offered a refund or the chance to rebook, while people currently booked for Sunday or Monday can rebook at no cost, subject to availability, the airline said.
Thomas Cook had been advising customers to “stay in their hotels until further notice”, but an updated statement from the company - which offers holidays to places such as Marmaris, Bodrum and Antalya - said: “Our flight and holiday programme is operating as normal and our staff on the ground in resort tell us that everything is calm and customers are enjoying their holidays.
“However, given the circumstances, we are offering free amendments and cancellations for all customers due to fly to Turkey today (Saturday July 16) and tomorrow (Sunday July 17).
“We are monitoring the situation closely and will update when we have further information.”
An easyJet spokeswoman said the airline did not expect any changes to its schedule, while Turkish Airlines advised passengers to check the latest flight information due to cancellations.
Thomson and First Choice flights to Dalaman, Antalya and Izmir are operating as normal.
In a statement they said: “Given these exceptional circumstances, customers due to depart on 16th July 2016 and who no longer wish to travel, can cancel and receive a full refund, or amend to another holiday currently on sale subject to availability.
“All flights departing on Monday 18th July 2016 are operating as normal.”
Advice on the Foreign Office website said: “There has been large-scale military action in Turkey, with the military deployed to the streets and widespread reports of gunfire and explosions in Ankara and Istanbul.
“The situation now appears quieter in Istanbul, and the bridges across the Bosphorus are reopening. But there are reports of tank fire and small arms fire in Ankara.
“Some flights to airports in Turkey are being diverted or cancelled. The road between Marmaris and Icmeler remains closed, following earlier reports of gunfire between the resorts of Marmaris and Icmeler.
“We strongly advise you to stay indoors, avoid public places, in particular demonstrations, and remain vigilant.”
The Foreign Office advised people due to travel to or from Turkey over the next few days to closely monitor travel advice and check with airlines or tour operators before travelling.
The UK’s largest travel association, Abta, said: “The vast majority of British travellers to Turkey will fly directly to the beach resorts on Turkey’s south coast which are hundreds of miles away from Istanbul and the capital Ankara.
“Abta estimates there are currently 50,000 people on holiday with its members in Turkey. There is no indication that guests in the coastal resorts are affected.”
The Foreign Office said more than 2.5 million British nationals visit Turkey every year.
But the tourism industry in Turkey has taken a hit due to recent terror attacks and the country’s proximity to Syria.
In its travel advice for Turkey, under the heading “Terrorism”, the Foreign Office says: “There is a high threat from terrorism. There is considered to be a heightened threat of terrorist attack globally against UK interests and British nationals, from groups or individuals motivated by the conflict in Iraq and Syria. You should be vigilant at this time.”